Method for controlling an internal combustion engine having a lambda regulation

ABSTRACT

The aim of the inventive method is to improve the emission values of an internal combustion engine during idling following a cold start. Said aim is achieved by inferring an adaptive value for the required fuel quantity from a characteristic curve in accordance with the temperature of the internal combustion engine and verifying during continuous lambda regulation whether predetermined adaptation conditions are met. If so, an adaptive value is determined from the parameters of the lambda regulator and the characteristic curve is adjusted according the newly determined adaptive value and the measured temperature of the internal combustion engine.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the U.S. National Stage of International ApplicationNo. PCT/EP2004/000269, filed Jan. 15, 2004 and claims the benefitthereof. The International Application claims the benefits of the Germanapplication No. 10307004.4, filed Feb. 19, 2003. The InternationalApplication and the German application are incorporated by referenceherein in their entirety.

FIELD OF INVENTION

The present invention relates to a method for controlling an internalcombustion engine having a lambda control.

BACKGROUND OF THE INVENTION

Internal combustion engines are subject to deviations in pilot mixturecontrolling due to the interaction of tolerances specific to individualsystem components such as, for example, injection valves, load sensors,etc. When mixture controlling has been activated by the lambda controland through mixture controlling while the internal combustion engine isat its operating temperature, the system tolerance will be minimized andsubsequently contribute only slightly to the internal combustionengine's emission characteristics. Only immediately after the internalcombustion engine starts do the system tolerances have a direct impacton its emission characteristics.

SUMMARY OF THE INVENTION

The only possible way to date to ensure effective pilot mixturecontrolling prior to the application of lambda controlling has been torestrict the tolerances for the system components depending on theircontribution to the emission characteristics. What is disadvantageoustherein is that very great accuracies in production have to be specifiedwhich significantly increase the costs.

An object of the invention is to provide a method for controlling aninternal combustion engine having a lambda control which method willreduce the emission of exhaust gas by simple means prior to theapplication of lambda controlling.

Said object is achieved by the claims.

With the method according to the invention a check is carried out in afirst phase after the internal combustion engine starts in order todetermine whether predefined activation conditions exist. If they do, anadaptive value will be determined for the internal combustion engine fordetermining the fuel mixture as a function of the measured temperaturevia a characteristic curve. The method is based on the knowledge thatpilot mixture controlling leads to deviations of varying intensity inthe combustion lambda, depending on the internal combustion engine'sstarting temperature, and hence to poorer emission values than in areference system. An adaptive value that takes account of the internalcombustion engine's temperature on starting is used in the methodaccording to the invention for determining the fuel mixture. Theactivation conditions ensure that the amount of fuel will only beadapted if the prerequisites for doing so exist, thus avoiding thesituation, for example, where the amount of fuel will be adapted duringa warm start.

In order to individually adjust the characteristic curve for theadaptive values as a function of the temperature, a check is carried outduring ongoing lambda controlling to determine whether predefinedadaptation conditions exist. If they do, an adaptive value will bedetermined from control parameters of the lambda control and thecharacteristic curve will be adjusted as a function of the newlydetermined adaptive value and of the internal combustion engine'smeasured temperature. The characteristic curve will thereby be adjustedto the internal combustion engine's particular characteristics byapplying the newly determined adaptive values. Ageing processes,system-component tolerances, and other specific characteristics of theinternal combustion engine will in particular also be registered throughthis procedure.

According to a preferred embodiment of the method one activationcondition is that the internal combustion engine starts cold and idles.It has been established that adaptive values can be determinedparticularly reliably from the control parameters of the lambda controlspecifically for the activation condition just cited. This is topractical effect geared to the control parameters' having assumed astable value. The adaptive value can also be calculated from the controlparameters once these have stabilized and/or when the lambda control hasoperated for longer than a predefined period. It has been establishedthat even a brief period of, say, 10–20 seconds following a cold startand before first drive-off will suffice to reliably determine theadaptive values from the control parameters of the lambda control.

The adaptive value is preferably determined from an integral portion ofthe lambda control. Pilot controlling can if necessary be correctedusing the integral portion, making it particularly suitable fordetermining the adaptive value prior to the application of lambdacontrolling.

In a preferred embodiment the characteristic curve is adapted and acomparison made with the adaptive values hitherto taken into account inthe characteristic curve. Through suitably selected calculation methodsit is ensured that an adaptive value so far removed from thecharacteristic curve will result directly in a major change to thecharacteristic curve.

The adaptive value is preferably weighted across the number ofcombustion cycles occurring since the start. Weighting of this type willtake account of the adaptive value's being suitable for cold conditionsof an internal combustion engine and of said value's preferably havingan increasingly lesser weighting as the number of combustion cyclesincreases and hence the internal combustion engine heats up.

BRIEF DESCRIPTION OF THE DRAWINGS

The method according to the invention will be explained in more detailbelow with the aid of a preferred instance.

DETAILED DESCRIPTION OF THE INVENTION

A check is carried out in a first step 10 after the internal combustionengine starts in order to determine whether the activation conditions(A) exist. As an activation condition it is checked whether the internalcombustion engine is idling and if a cold start is taking place. Themethod thus launches in an idling phase following starting while theinternal combustion engine is not at its operating temperature. Thelambda probes not being operable while the internal combustion engine isin this state, the air/fuel mixture cannot yet be regulated.

An adaptive value is determined from a characteristic curve in anensuing step 12. The internal combustion engine's temperature is forthis purpose measured in step 12 and the corresponding adaptive valueread out in the characteristic curve applied across the temperature. Theadaptive value indicates how the injected amount of fuel is to beadjusted to the operating temperature. A basic value for an amount offuel, for example, can be specified for this that is raised or loweredby the adaptive value as a function of the internal combustion engine'soperating temperature.

The adaptive value is weighted in step 14 to allow for the fact that theinternal combustion engine's temperature increases over time and hencewith the combustion cycles. As an instance of weighting it can beprovided for the adaptive value initially to be entered having theweighting 1 and after, say, 800 combustion cycles to be rated onlyhaving the weighting 0.2.

The amount of fuel is calculated according to the adaptive value in step16 and injected.

A check is carried out in a second phase of the exemplary embodiment todetermine whether the adaptation conditions (B) exist. In the secondphase the characteristic curve is adjusted to the internal combustionengine's particular characteristics. As an adaptation condition it ischecked whether the internal combustion engine will continue idling onapplication of lambda controlling. In this case a mixture-adaptationvalue will be determined from the I portion of the lambda control via alow-pass filtering operation. A check is carried out in step 22 for theadaptive value calculated in step 20 to determine whether this is a newadaptive value, with “new adaptive value” meaning that an adaptive valuesuitable for adjusting the characteristic curve was calculated at all instep 20. A further check is carried out to determine whether the Iportion of the lambda control has already sufficiently stabilized to beable to reliably determine the adaptive value therefrom. If not, themethod will be terminated without the characteristic curve's having beenadapted.

A new adaptive value possibly determined as being present in step 22will then be stored in the characteristic curve, with knowninterpolation or, as the case may be, extrapolation methods preferablybeing applied to reliably obtain a characteristic curve from thedetermined adaptive values.

The method according to the invention will terminate at step 26 when thecharacteristic curve has been adapted.

If the internal combustion engine is restarted at some subsequent timeunder comparable temperature conditions and if the activation conditionshave been met, the previously determined adaptive value will beinitiated with the stored value immediately after the transition fromstart to idling and included in pilot mixture controlling. Weightingacross the combustion cycles occurring up to that moment willadditionally take place before the adaptive value is converted into anamount of injected fuel. This is because the influence of an impreciseinjected amount on mixture deviation does not progress linearly withrunning time following a cold start. Compensating of mixture deviationtaking place in this way will continue being taken into account for aslong as the activation conditions are met or until the method changesover to the adaptation phase. It is thus ensured that adapting will alsobe carried out in response to changing system characteristics over thelife of the components and that this will not result in poorer emissionvalues.

If no adaptive values have been previously determined, the initializingvalue from the family of adaptation characteristics will be used. Theadaptive values can likewise be re-initialized for example following arepair or after a component has been replaced. The method according tothe invention offers the following advantages:

-   -   lower emissions with the same tolerance requirements placed on        the system components,    -   more stable emission characteristics as components age,    -   avoidance of what is termed the green effect where using a new        component results in an abrupt change in system characteristics.

The adaptive values are furthermore also a measure of the effectivenessof the temperature-raising measures performed on the catalyticconverter. Significant deviations in the adaptive values can thus alsobe used to diagnose the cold-start strategy and for raising thetemperature of the catalytic converter.

1. A method of controlling an internal combustion engine having a lambdacontrol, the method comprising: determining if predefined activationconditions are met upon starting the combustion engine by executing afirst check procedure; measuring an internal temperature of thecombustion engine and determining an adaptive value using acharacteristic curve for calculating a fuel mixture based on themeasured internal temperature, if the first check procedure is positive,the characteristic curve including a progression of the adaptive valuerelative to a progression of the internal temperature; determining ifpredefined adaptation conditions are met while the lambda control is inoperation by executing a second check procedure; and determining anupdated adaptive value using at least one control parameter of thelambda control and adjusting the characteristic curve using the updatedadaptive value and the measured internal temperature, if the secondcheck procedure is positive, and maintaining the unadjustedcharacteristic curve, if the second check procedure is negative, whereinthe updated adaptive value is weighted by a weighting parameter duringeach combustion cycle until the lambda control is in effect.
 2. Themethod according to claim 1, wherein the activation conditions includethe conditions that the internal combustion engine has been started at atemperature below a predefined temperature, and that the internalcombustion engine is idling.
 3. The method according to claim 1, whereinthe adaptation conditions include the condition that the internalcombustion engine is idling.
 4. The method according to claim 1, whereinthe adaptive value is calculated using at least one robust controlparameter of the lambda control.
 5. The method according to claim 4,wherein the robust control parameter is determined from at least one ofa plurality of control parameters of the lambda control after a currentvalue of the at least one control parameters has completed transientoscillation.
 6. The method according to claim 4, wherein the robustcontrol parameter is determined from at least one of a plurality ofcontrol parameters of the lambda control after the lambda control hasbeen operating for at least a predefined minimum operating period. 7.The method according to claims 3, wherein the at least one controlparameter of the lambda control is an integral portion included in thelambda control.
 8. The method according to claim 4, wherein determiningthe updated adaptive value is further based on at least one previouslyupdated adaptive value.
 9. The method according to claim 2, wherein theweighting parameter is decreased during each combustion cycle followinga preceding combustion cycle.